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I've acquired all the parts to build a Reprap Prusa i3 rework, the only missing part is the frame.

I'm in doubt between a MDF cut (cheaper) or acrylic (more expensive), of course a cheaper one is my preferred option until I see any disadvantage on making it of wood.

I thought about variables like heat and humidity and the possibility of expansion/contraction of the frame, is this a valid concern? Will I have more precision buying the acrylic one or is it irrelevant?

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    $\begingroup$ Acrylic is a poor choice for anything structural. It cracks and snaps under any sort of pressure. Tightening screws in it is a game of chicken. MDF is much better on almost every front. $\endgroup$ – John Meacham Aug 8 '16 at 3:08
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Generally speaking, MDF will weather OK. In areas of high humidity you might experience warpage, but you can mitigate that by sealing the surface with paint or varnish. However you will probably find that of the two materials, acrylic will be more stable over a few years.

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I want to add the following to the already direct and very good answer of @Dani Epstein. It does not answer your question, but hopefully may help many people who are reading the question when choosing between the two materials.

Acrylic is less stable and will probably wear off faster than a well-built MDF frame for a 3D printer! I will address the points separately.

  1. An MDF frame has much(!) more mass than acrylic, which will reduce vibrations immediately. Almost more important, a box frame, as typical for the Prusa i3 for example, stabilizes itself intrinsically more by its 'redundant wall' design (don't beat me up over the wording here, I didn't find a better way to describe the property that results from the towers.)
    Compare these two images taken from reprap wiki Prusa i3: boxframe (from reprap-wiki) metal frame (from reprap-wiki) You will probably not find an acrylic frame with this design. Shear stress as produced by the moving carriages, as well as z-wobble from the rods should theoretically be much less.
  2. The acrylic might not wear by 'natural causes' since it is not a biologic material as wood is, but it will wear much faster due to handling the material, maintenance and human errors. The material is very brittle. You can find lots of reports on the web where the frame cracked or broke during setup. Here is my favorite example from someone with a lot of experience (1:20-2:30): https://www.youtube.com/watch?v=wkkVk8c8XoU
  3. Acrylic is a bad choice in terms of its mechanical properties: It is soft (I found low tensile strength as a number to compare in the given database), has lots of thermal expansion (5 times higher than stainless steel) and melts at 160 C (so beware of anything touching your hotend). Feel free to compare it to other materials here (no MDF or plywood in that database, though ;-) ): http://www.goodfellow.com/E/Polymethylmethacrylate.html

This altogether makes acrylic a very bad choice for a 3d printer frame material in my opinion. Choose MDF or plywood, you can make it look cool by painting it, too.

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  • $\begingroup$ Yeah, I have so many cracked acrylic parts from previous builds. I have no idea why anyone thought it would be a good thing for 3d printers other than it is dead easy to Lasercut with relatively inexpensive cutters. $\endgroup$ – John Meacham Aug 8 '16 at 3:11

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